Lua VM initialization hook

[BenMcAvoy]

It would be nice of IMod had a callback for Lua VM initialization so that mods that add Lua APIs could have a nicer experience

[BenMcAvoy]

Note, lua.h defines lua_h. We could use a type alias to a PVOID when lua.h is not included to prevent forced requirements of Lua to be installed.

E.g.

#ifndef lua_h
typedef struct lua_State lua_State;
#endif

[VeraDev0]

Cant we just create our own lua.h file where it has everything in it meaning the modder can just do this and immediately get access to the lua api without needing to include or install luajit

#include <rivet/lua.h>

// You now got access to the lua c api, no need to link any other libraries

[BenMcAvoy]

Cant we just create our own lua.h file where it has everything in it meaning the modder can just do this and immediately get access to the lua api without needing to include or install luajit

You mean we create loads of function pointers and stuff?
E.g. in rivet/lua.h there's PushCFunction_t lua_pushcfunction = nullptr;?

[VeraDev0]

Cant we just create our own lua.h file where it has everything in it meaning the modder can just do this and immediately get access to the lua api without needing to include or install luajit

You mean we create loads of function pointers and stuff?
E.g. in rivet/lua.h there's PushCFunction_t lua_pushcfunction = nullptr;?

That's basically it really, and rivet would just populate those nullptr's with pointers to the actual lua51.dll functions. We probably can even make a dynamic generator for this in case Scrap Mechanic ever updates the LuaJIT library to a newer version that may have the functions changed.

(However i don't expect this to really happen, based on that for some reason they are still using Visual Studio 2015 to compile Scrap Mechanic in 2025)

[BenMcAvoy]

https://github.com/ScrappySM/CarbonLib/blob/main/CarbonLib/include/carbon/lua/lua.h

[BenMcAvoy]

There are currently a few techniques for this:

• Sig scanning for the Lua registrations table
• IAT hooking a Lua function such as loadstring
• Minhooking LuaVM::LuaVM

[BenMcAvoy]

Sig scanning for the registration table is not feasible. However, I do like the idea of adding an entry to this table.

One approach is to search for the string "\nfunction class" in .rdata. Then you can xref this into .text which will get you into the first registration function. Use unwind information to get the start address of this function and then cross reference into .rdata again. You now have the address of the table.